1. Field of the Invention
The present invention generally relates to an apparatus and method generally useful for holding one or more electrodes of precisely known exposed surface area. The present invention is particularly useful in a device for determining under a variety of conditions the corrosion properties of the material from which the electrode has been formed. More particularly, the present invention relates to a device for holding the described electrodes by a means which only infinitesimally decreases the exposed surface area of the electrodes and which is characterized by an exposed electrically conductive surface area which is small relative to the surface area of the test electrode.
2. Description of the Background
It is often desirable to determine the corrosion characteristics of materials under a variety of conditions simulating the working environment where devices constructed of the materials are projected to be employed. It will be appreciated by those skilled in the art that these tests are conveniently conducted on test electrodes formed of the materials. In conducting these tests, the test electrodes are exposed to conditions simulating the projected working environment or often to conditions simulating the most severe conditions to which the materials are expected to be exposed. For example, corrosion tests of materials used to construct or in connection with downhole devices are preferably performed in a simulated downhole environment. These tests are typically conducted in the presence of drilling muds and at extremely high temperatures and pressures. In fact, temperatures approaching 450.degree. F. and pressures in excess of 10,000 psi are not uncommon. Further, these tests are often performed in the presence of corrosive fluids, e.g., hydrogen sulfide, which might be encountered in drilling operations.
The corrosion test electrodes employed for these determinations are often electrically isolated from their environment. Alternatively, a working voltage is applied to the test electrodes. In order to correctly analyze the effects of corrosion on a test electrode, including calculation of the corrosion rate under various conditions of temperature, pressure and the like, it is necessary that the surface area of the test electrode exposed to the test conditions be precisely known. These test methods have required the production of electrodes of precisely known exposed surface area. Typically, these electrodes are manufactured in the shape of rods. These rods are maintained in the test device by insertion into appropriate chucks or bores which have significantly and non-reproducibly altered the exposed surface area. The non-reproducibility of the surface area remaining exposed in these devices has reduced the accuracy of corrosion effect data obtained by these methods.
Accordingly, there has been a long felt but unfulfilled need within the testing industry for a corrosion test electrode holder which securely engages a plurality of test electrodes in a manner resulting in the engaged electrodes having precisely known exposed surface areas.